If you need the best image quality for DVR Spy Cams, you will certainly have to turn to wired surveillance units or coaxial surveillance cameras. They may still be the most reliable today compared to IP video cameras. Indeed they are much more difficult to pirate from the outside. Analog cameras are generally the most suitable for large-scale outdoor systems (buildings or public places).
If you want a quickly usable system that does not require work or wall holes, then this type of camera connected to a network may be for you. Ethernet cable IP cameras are preferred in the case of large outdoor systems. The risk of excessive Wi-Fi interference would make this other type of video camera too unreliable.
Dummy surveillance cameras are certainly the cheapest cameras on the market, but also the least reliable. The goal is to deter the perpetrator, this type of device is designed to be as ostentatious as possible, including at night.